Is unlocking 4th and 5th axis nessary

[CireArts]

Was wondering if it is necessary in a program to issue a M11 and M13 before any B and C axis moves..

[Mecanix]

All depending on the controller you have and how the axis' params are set. Most modern controls can do this automatically.
Although params for automated clamping isn't the most popular feature. Instead a pre-motion eval method is normally hard-coded at the postprocessing level for the clamping M events, allowing both simultaneous (no clamping) AND off-center roughing (clamping) on the same machine-tool. This frees the operator from having to modify the controller params before a job (safer assumption from the CAM programmer end).